The present invention relates to improved devices for collecting body fluids such as blood, for example.
Blood collection is a routine aspect of medical diagnosis and treatment. It has been found that it is often preferable to provide a collection chamber which is at least partly evacuated to facilitate collection of blood samples. The subatmospheric pressure of the chamber serves as an aid to draw blood from the patient through a conduit, such as a needle for example, into the collection chamber. In the past, it has been common practice to provide pre-evacuated chambers for the collection of blood samples.
Such pre-evacuated chambers are sold as partially evacuated glass tubes which are closed by a pierceable diaphragm. In use, a double-ended needle is placed with one end in a patient's vein and then the other end of the double-ended needle is passed through the pierceable diaphragm into the interior of the collection tube. Subatmospheric pressure inside the tube then acts to draw blood through the needle into the tube.
The use of such pre-evacuated chambers brings with it certain disadvantages. Because the tubes must be stored for extended periods of time after they have been evacuated, it is possible for a slow air leak to destroy the vacuum in the chamber over an extended period of time. Such leakage can result in contamination of the tube when contaminants are brought into the tube by the leaking air. In addition, such leakage presents a reliability problem, because once the vacuum inside the tube is lost the tube must be discarded. Moreover, the vacuum in pre-evacuated collection tubes cannot be adjusted for collection of differing amounts of blood. Thus, it is often necessary to supply and stock several sizes of collection tubes to accomodate the varying needs.